Dear all,

I was operating a GE Fr5 machine with GE speedtronic-Mark5 controls, familiar with speed ratio valve and Gas control valve operation.

But now as I joined in another power plant where GE Fram9FA machine is being erected with speedtronic Mark6 controls. Here I saw a number of control valves in Gas fuel compartment, like VSR, VGC1/2/3, ASV, 20VG1/2/3,20PG 5/6 etc. This unit have only gas fuel operation (not due fuel), with DLN2 combustors.

Can someone may please help me understand why so many valves when only one speed ratio valve and one gas control valve is enough for operation.
I hope you can explain in brief the gas fuel operation in Fr9FA.

Thanks in advance.
regards
Bab.jana

 

Well, the new machine you will be working on should be provided with P&IDs (Piping Schematic drawings, in GE-speak) which would greatly help you in understanding the differences between the machines.

Essentially, the machine you were working on had a conventional combustion system, with a single fuel nozzle in each combustor. The fuel was burned using a diffusion flame in each combustor, and this produced a very high "flame" temperature, which results in very high NOx formation and emissions, including CO2.

The new machine you will be working on has multiple fuel nozzles in each combustor, and they are supplied by manifolds to which the various gas fuel control valves are connected. As the unit is started, loaded, and unloaded, fuel will be switched by the Speedtronic to various fuel nozzles and combinations of fuel nozzles in order to keep the emissions (NOx, particularly) as low as possible. This is sometimes called "staging" of the fuel supply, but not always. The various combinations of fuel nozzles are called combustion "modes".

In a DLN 2.n configuration, GE maintains the fuel is premixed (for reduced emissions) in all combustion modes (stages). As the fuel is "staged" the small diffusion flame at the tip of each fuel nozzle will be lit or extinguished, depending on whether fuel is flowing through that nozzle or not. Some of the fuel exits the nozzle before the tip (where the diffusion flame exists), and it's that fuel that is premixed with combustion air and results in the lower "firing temperature" (which is the flame temperature in this case, not to be confused with the other "firing temperature" which is the temperature of the combustion gases leaving the first stage turbine nozzle....).

ASV probably refers to Auxiliary Stop Valve, which is a valve upstream of the gas control valves that serves as a sure-acting stop valve.

There will likely be multiple gas fuel purge lines, hence the purge solenoids 20PG-5 and -6. There will likely be multiple areas of the gas fuel piping to be vented during a shutdown/trip, hence the 20VG-1, -2, & -3. I believe there is still a speed-ratio valve for DLN2.0 combustion systems, hence the VSR (Valve-Speed/Ratio).

The three gas control valves, VGC-1, -2 & -3, will be used to stage the fuel to the various manifolds and nozzles during the starting, loading, and unloading of the unit.

Again, you should obtain copies of the P&IDs and study them to become familiar with the differences between the Frame 5 and the new unit you will be working on. Among them, you will find that there will be two AC motor-driven L.O. Pumps and two AC motor-drive Hydraulic Pumps. This is because there is typically no Accessory Gear on F-class turbines, so there are redundant AC motor-driven pumps.

Also, there will be no Load, or Reduction, Gear as the turbine will be directly connected to the generator rotor and will spin at 3000 RPM (which corresponds to 50 Hz for a two-pole synchronous generator).

The unit will likely use a turning gear mechanism for cooldown, instead of a hydraulic ratchet.

Lastly, the unit will be started by temporarily converting the generator to an electric motor and using the "motor" to crank, purge, and accelerate the unit up to approximately 95% speed, at which time it will be switched back to a generator. Sometimes this is referred to as a "static starter" or an "LCI" (Load-Commutated Inverter) or one of several other terms.

All of this happens automatically, via the Speedtronic (probably a Mark VIe if this is a new unit being constructed on site).

Enjoy! This is a good opportunity, and a lot of your experience will translate directly. You shouldn't have to learn any new terms for unit modes and operation. OFF, CRANK, FIRE, AUTO, REMOTE; BASE; PRESELECT; etc., should all be the same as you're accustomed to.

Best of luck!

 

Thank you sir for your brief description. As you said I will definitely get the P&ID for the gas system (but so far I could not).

Meanwhile I came across on the net a good GE document on DLN1 and DLN2, GER-3568G, which is explaining clearly the modalities of all the controls involved along with line sketch.